Formatted question description: https://leetcode.ca/all/1357.html

# 1357. Apply Discount Every n Orders (Medium)

There is a sale in a supermarket, there will be a discount every n customer.
There are some products in the supermarket where the id of the i-th product is products[i] and the price per unit of this product is prices[i].
The system will count the number of customers and when the n-th customer arrive he/she will have a discount on the bill. (i.e if the cost is x the new cost is x - (discount * x) / 100). Then the system will start counting customers again.
The customer orders a certain amount of each product where product[i] is the id of the i-th product the customer ordered and amount[i] is the number of units the customer ordered of that product.

Implement the Cashier class:

• Cashier(int n, int discount, int[] products, int[] prices) Initializes the object with n, the discount, the products and their prices.
• double getBill(int[] product, int[] amount) returns the value of the bill and apply the discount if needed. Answers within 10^-5 of the actual value will be accepted as correct.

Example 1:

Input
["Cashier","getBill","getBill","getBill","getBill","getBill","getBill","getBill"]
[[3,50,[1,2,3,4,5,6,7],[100,200,300,400,300,200,100]],[[1,2],[1,2]],[[3,7],[10,10]],[[1,2,3,4,5,6,7],[1,1,1,1,1,1,1]],[,],[[7,3],[10,10]],[[7,5,3,1,6,4,2],[10,10,10,9,9,9,7]],[[2,3,5],[5,3,2]]]
Output
[null,500.0,4000.0,800.0,4000.0,4000.0,7350.0,2500.0]
Explanation
Cashier cashier = new Cashier(3,50,[1,2,3,4,5,6,7],[100,200,300,400,300,200,100]);
cashier.getBill([1,2],[1,2]);                        // return 500.0, bill = 1 * 100 + 2 * 200 = 500.
cashier.getBill([3,7],[10,10]);                      // return 4000.0
cashier.getBill([1,2,3,4,5,6,7],[1,1,1,1,1,1,1]);    // return 800.0, The bill was 1600.0 but as this is the third customer, he has a discount of 50% which means his bill is only 1600 - 1600 * (50 / 100) = 800.
cashier.getBill(,);                           // return 4000.0
cashier.getBill([7,3],[10,10]);                      // return 4000.0
cashier.getBill([7,5,3,1,6,4,2],[10,10,10,9,9,9,7]); // return 7350.0, Bill was 14700.0 but as the system counted three more customers, he will have a 50% discount and the bill becomes 7350.0
cashier.getBill([2,3,5],[5,3,2]);                    // return 2500.0


Constraints:

• 1 <= n <= 10^4
• 0 <= discount <= 100
• 1 <= products.length <= 200
• 1 <= products[i] <= 200
• There are not repeated elements in the array products.
• prices.length == products.length
• 1 <= prices[i] <= 1000
• 1 <= product.length <= products.length
• product[i] exists in products.
• amount.length == product.length
• 1 <= amount[i] <= 1000
• At most 1000 calls will be made to getBill.
• Answers within 10^-5 of the actual value will be accepted as correct.

Related Topics:
Design

## Solution 1.

// OJ: https://leetcode.com/problems/apply-discount-every-n-orders/

// Time:
//      getBill: O(N) where N is the count of product the customer bought
// Space: O(P)
class Cashier {
int num = 0, n, discount;
unordered_map<int, int> m;
public:
Cashier(int n, int discount, vector<int>& products, vector<int>& prices) : n(n), discount(discount) {
for (int i = 0; i < products.size(); ++i) m[products[i]] = prices[i];
}
double getBill(vector<int> product, vector<int> amount) {
double p = 0;
for (int i = 0; i < product.size(); ++i) p += m[product[i]] * amount[i];
if (++num % n == 0) p -= (discount * p) / 100;
return p;
}
};